SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Journal of the Optical Society of America. A, Optics, image science, and vision

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In this paper, a biologically inspired multilevel approach for simultaneously detecting multiple independently moving targets from airborne forward-looking infrared (FLIR) sequences is proposed. Due to the moving platform, low contrast infrared images, and nonrepeatability of the target signature, moving targets detection from FLIR sequences is still an open problem. Avoiding six parameter affine or eight parameter planar projective transformation matrix estimation of two adjacent frames, which are utilized by existing moving targets detection approaches to cope with the moving infrared camera and have become the bottleneck for the further elevation of the moving targets detection performance, the proposed moving targets detection approach comprises three sequential modules: motion perception for efficiently extracting motion cues, attended motion views extraction for coarsely localizing moving targets, and appearance perception in the local attended motion views for accurately detecting moving targets. Experimental results demonstrate that the proposed approach is efficient and outperforms the compared state-of-the-art approaches.

Concepts: Mathematics, Detection theory, Open problem, Open problems, Infrared photography, Film and video technology, Infrared imaging, Infra-red search and track

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A recently published sparse spectrum (SS) model of the phase front perturbations by atmospheric turbulence [J. Opt. Soc. Am. A30, 479 (2013)] is based on the trigonometric series with discrete random support. The SS model enables fewer computational efforts, while preserving the wide range of scales typically associated with turbulence perturbations. We present an improved version of the SS model that accurately reproduces the power-law spectral density of the phase fluctuations in the arbitrary wide spectral band. We examine the higher-order statistics of the SS phase samples for four versions of the SS model. We also present the calculations of the long-exposure Strehl numbers and scintillation index for the different versions of the SS model. A nonoverlapping SS model with a log-uniform partition emerges as the most appropriate for the atmospheric turbulence representation.

Concepts: Mathematics, Fundamental physics concepts, Fluid dynamics, Aerodynamics, Spectrum, Turbulence, Wake turbulence, Astronomical seeing

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In this work, we generalize the paraxial ray-tracing formulas to include nonparaxial rays. For a refracting (reflecting) spherical surface, a new single meridional formula is derived. This formula can be easily reduced to a paraxial formula. It can also be applied to any aspheric (or general) surface with a known equation. Also, a new exact ray-tracing procedure for a centered system of spherical surfaces is derived. In this procedure, we apply just two simple equations for each surface of the system, which, to the best of our knowledge, makes it the shortest analytical ray-tracing technique ever. This procedure can be applied in some other applications. For example, it can be reduced to a new single paraxial formula that can be easily used to trace a paraxial ray propagating through a system of spherical surfaces. Also, it is applied to derive an exact meridional formula for both thick and thin lenses that can also be reduced to a new paraxial formula different from the Gaussian one. These results led us to easily derive an exact formula for the longitudinal spherical aberration for both thick and thin lenses and also for a single refracting (reflecting) spherical surface. Numerical examples are provided and discussed.

Concepts: Optics, Volume, Science, Lens, Geometrical optics, Expression, Torus, Ray

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With aging, the human retina undergoes cell death and additional structural changes that can increase scattered light. We quantified the effect of normative aging on multiply scattered light returning from the human fundus. As expected, there was an increase of multiply scattered light associated with aging, and this is consistent with the histological changes that occur in the fundus of individuals before developing age-related macular degeneration. This increase in scattered light with aging cannot be attributed to retinal reflectivity, anterior segment scatter, or pupil diameter.

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The electromagnetic enhancement by a metallic nanowire optical antenna on metallic substrate is investigated theoretically. By considering the excitation and multiple scattering of surface plasmon polaritons in the nanogap between the antenna and the substrate, we build up an intuitive and comprehensive model that provides semianalytical expressions for the electromagnetic field in the nanogap to achieve an understanding of the mechanism of electromagnetic enhancement. Our results show that antennas with short lengths that support the lowest order of resonance can achieve a high electric-field enhancement factor over a large range of incidence angles. Two phase-matching conditions are derived from the model for predicting the antenna lengths at resonance. Excitation of symmetric or antisymmetric localized surface plasmon resonance is further explained with the model. The model also shows superior computational efficiency compared to the full-wave numerical method when scanning the antenna length, the incidence angle, or the wavelength.

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The two new kinds of truncated Gaussian beams, known as the half and quarter Gaussian beams, are defined as the product of the fundamental Gaussian beam with the Heaviside unit step function. Using the generalized Collins integral, the exact analytical propagation formulas are derived for the truncated Gaussian beams through paraxial optical systems. Combined with the Gaussian beam decomposition method, the truncated Gaussian beams are used to represent the sharp edges of a field after a hard aperture. The modified Gaussian beam decomposition method presented in this work enables the calculation of the diffraction of a given field from a hard aperture with an arbitrary shape. This solves one of the limitations of the conventional Gaussian beam decomposition method, which is its inability to accurately model the diffraction of fields with sharp edges, especially in the near field. The validity and accuracy of the proposed method are demonstrated using a few exemplary diffraction calculations.

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We describe the design, construction, calibration, and characterization of a multi-primary high dynamic range (MPHDR) display system for use in vision research. The MPHDR display is the first system to our knowledge to allowfor spatially controllable, high dynamic range stimulus generation using multiple primaries.We demonstrate the high luminance, high dynamic range, and wide color gamut output of the MPHDR display. During characterization, the MPHDR display achieved a maximum luminance of 3200 cd=m2, a maximum contrast range of 3; 240; 000 V 1, and an expanded color gamut tailored to dedicated vision research tasks that spans beyond traditional sRGB displays. We discuss how the MPHDR display could be optimized for psychophysical experiments with photoreceptor isolating stimuli achieved through the method of silent substitution. We present an example case of a range of metameric pairs of melanopsin isolating stimuli across different luminance levels, from an available melanopsin contrast of117%at 75 cd=m2 to a melanopsin contrast of23%at 2000 cd=m2.

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A three-dimensional laser scanner has been designed and widely utilized in many fields. The lens plane is tilted according to the Scheimpflug condition and the optical axis is not perpendicular to the charge-coupled device plane. In this case, depth of view can be extended significantly. In this paper, analytical models for a camera with a tilted lens and a laser scanner meeting the Scheimpflug condition are presented. Based on these models, a calibration procedure is detailed. We propose a simple calibration method to determine the intrinsic parameters of a Scheimpflug camera. Meanwhile, two calibration methods for a laser scanner in the Scheimpflug condition are detailed. According to the obtained intrinsic parameters, the laser scanner can be calibrated directly. Moreover, a simple calibration for a three-dimensional laser scanner without the help of a precise positioning system is described. Experimental results show the effectiveness and high measurement accuracy of our calibration methods.

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This paper presents a model-based approach to adaptive optics (AO) control based on a zonal (i.e., pixelized) representation of the incoming atmospheric turbulence. Describing the turbulence on a zonal basis enables the encapsulation of the standard frozen-flow assumption into a control-oriented model. A multilayer zonal model is proposed for single-conjugate AO (SCAO) systems. It includes an edge compensation mechanism involving limited support, which results in a sparser model structure. To further reduce the computational complexity, new resultant zonal models localized in the telescope pupil are proposed, with AR1 or AR2 structures, that match the spatial and temporal cross-correlations of the incoming turbulence. The global performance of the resulting linear quadratic Gaussian (LQG) regulator is evaluated using end-to-end simulations and compared to several existing controllers for two different configurations: a very large telescope SCAO and low earth orbit satellite tracking. The results show the high potential of the new approach and highlight possible trade-offs between the performance and complexity.